This project has been crippled because of electronic unreliability in the impedance detection instrument and in the computer, which has had regular breakdowns and poor service. Dr. Tom Lewis has effected changes to correct this situation. The work to date has shown the promise of impedance detection of bacterial growth. Major advantages over radioactive methods are safety, economy, and freedom from disposal problems. Impedance growth curves are characteristic and reproductible for many of the test strains. This finding was unexpected and demands further investigation. Impedance response to bacterial growth as a phenomenon is complex and little understood. There are probably a number of competing electrical phenomena, and a number of ways that these affect electrodes, which become "coated" during growth, such that detection of further impedance resonse is severely blunted. Impedance growth curves vary greatly between bacterial species. Brucella abortus provides a very slow, steady millivolt response such that the computer does not signal the culture positive until the population density is 1x10 to the 6th power bacteria/ml. Escherichia coli lowers impedance sufficiently at 1x10 to the 4th power/ml to signal a positive culture. Since automation is the price consideration at this time for using impedance detection, this large difference is not critical in early growth detection, since because of continuous monitoring, even the slow response usually prompts a positive signal long before visual detection would be likely.